Process for electrolytic reduction of pentionic acid lactones



Patented Jan. 4, 1949 UNITED STATES PATENT OFFICE j PROCESS FOR ELECTROLYTIC REDUCTION F PENTONIC ACID LACTONES Hans Spiegelberg, Basel, Switzerland, assignor to Hofimann-La Roche Inc.,.Nutley, N. .L, a cor-. poration of New Jersey 7 No Drawing. Application January 18, 1946, Serial. 1 No. 642,111. In Switzerland November 10, 1944 Section 1, Public Law 690, August a, 1946 y Patent expires November 10, 1964 10 c aims. (chaos-77) Reduction of lacton'es of poly-hydroxy-car- The troublesome manufacture of the amalgamby carryingisodium into the mercury, during which i procedure the mercury is locally heated to high temperature by the vehement reaction accompanied by fire-phenomena, maybe avoided by electrochemical preparation of the amalgam.

However, this method, too, requires great quantitles of mercury. According to the present invention, lactones of poly-hydroxy-carbonic acids may be reduced at separating at the amalgam cathodetakes par inthereduction of the lactone.

It is advantageous to eflfect the reduction, according to the present invention, in the presence of boric acid. The yields are thus higher and l more equable and disadvantageous influences of impurities in the mercury are considerably reduced. It is recommendable to carryout the reaction at a temperature'between +10 and +12 C.

According to the present invention high quantitles of lactones may bereduced in equable high yields with comparatively small amounts of mercury, since amercury layer of only a few millimetres height is suificient' for the formation of the cathode. It is a further advantage of the electrolytic method that one is free, according to the selection of the electrolyte, to select the amalgam mercury-cathodes, ii the electrolyte contains the salt of a metal apt to form an amalgam. The lactone is dissolved in a suitable catholyte in an electrolysing apparatus/the electrode rooms of which preferably are separated by a diaphragm (for instance made of clay). Aqueous solutions of alkali and zinc salts or of mixtures of these metals are especially suitable as electrolytes.

In the process according to the present invention the electrolytically formed sodium amalgam acts as reducing agent. Consequentto the con-.

sumption of amalgam during the reduction a metal hydroxide, for instance alkali hydroxide when using alkali amalgam, is formed. Appropriately, the hydrogen-iomconcentration in the cathode room is kept substantially constant by continuous neutralisation of the base formedj this may, for instance, be eflectedby dropwise addition of acid into thecatho'deroom. Iti's advisable to use for this neutralisation an acid containing the same anion as the salt employed for the preparation of the electrolyte; thiscauses the concentration of the electrolyte solution to remain substantially constant and the amalgam to be regenerated continuously. Since it has been found in practice thatthe quantity of acidneeded for the neutralisation of the base is far lower than the quantitycalculat'edfrom the electric current passed through the apparatus, it must be assumed that at least part of the hydrogen electrolytically or amalgam mixure's from a great variety of these substances. Thus; the reduction of lactones of poly-hydroxy-carbonic acids may, for instance, be effected at a sodium amalgam or potassium amalgam or a mixed potassium-sodiumamalgam or sodium -zinc amal'gam cathode.

Example 1 The electrolysing apparatus consists of a glass vessel at the bottom of which is the mercury oath The electric current is conducted to the cathode by a graphite rod placed in a glass tube in order to isolate thesame against the catholyte. A clay cell which takes up the anolyte, is: hung into the glass vessel in such a manner that the bottom of the cell is placed a few centimetres above themercury cathode. A platinum wire-net covering the floor ofthe clay cell serves as anode. The catholyte is cooled by means of an enamelled iron worm. Speedy circulation of the catholyte between the-floor'of'the clay cell-and the mercury cathode is a'chievedby an effective stirrer.

A'l5% aqueous sulphuric acid is poured into the clay cell while pure mercury and a solution of 600 parts by weight of crystallised sodium sulphatein 3000 parts of water are passed into the cathode room. In order to reach the appropriate concentration of amalgam, the sodium sulphate solution is first electrolysed alone for one hour with 40 amperes at a current densityof' about 20 amperes per ama; After. termination of this primary electrolysis, 300 parts by weight of ribolactone and 200 parts by Weight of .boric acid are added to thecatholyte and electrolysisv is continued with unchanged current. density. The. temperature of the catholyte shouldbe. below +12 C., preferably lo'etween +5 and +l 2 C. By dropping in dilute sulphuric acid; the solution is made weakly the conditions-given in Example 1'.

acid to Congo paper (the said paper showing bluegreyish colour). The ribose content of the catholyte ismeasured fromtime to time by determination corresponding to Fehling; The maximum is reached within 4 to 4 hours. Electrolh ysis is then broken off. For further batches no primary electrolysis is necessary, since the sodium content of the amalgam at the end of the' first process is sufficient to start further electrolysis. I

The isolation of the ribose from the electrolyte may, for instance, be effected as follows: The

the apparatus described in Example 1. catholyt'e consists of a solution of 300 parts by are reduced at a sodium-amalgam electrode in The weight of sodium sulphate in 1500 parts of water. 'In order to form the amalgam cathode, this'solution is electrolysed during one hour at 20 amperes,

electrolyte is madeweakly 'acidtonlitmus and, i

then concentrated in vacuo to 1200 parts by volume at moderate temperature. Parts of the, boric acid crystallise out and are separatedby. In the filtrate, the sodium suction filtration.

the cathode current density being amperes per' dm.

After termination of this primary electrolysis, 150 parts by Weight of d-arabonic acid sulphate is precipitated by addition of 2000 parts by volume of spirit and filtered off. The alcoholic ribose solution is concentrated to 2000 parts by volume, rendered alkaline to; litmus by'addition of sodium hydroxide and then againv acidified by means of acetic acid. From thissolution ribose is precipitated as the p-bromo-phenyl-hydrazone by stirring for 12 hours at room temperature with 250 parts by weight of p-bromo-phenylhydrazine. About 385partsby weightof crude d-ribose-p-bromo-phenyl-hydrazone are .obtained which after recrystallisation from absolute alcohol yield 360 parts by weight of the pure product melting at 167 C.- j Ribose may be obtained from'the ribose-p-i bromo-phenyl-hydrazone by cleavage with, benialdehyde according to known methods (see, for

instance, P. Karrer and coworkers, Helvetica.

Chimica Acta, vol 18, 1935, p. l445; a ndM. Steiger, Helvetica Chimica Acta, vol. 19, 1936, p.195); 1

Example 2 300 parts by weight of d-ribonic' acid lactone are reduced at a potassiumamalgamcathode in the apparatus described in Example 1. All

i working conditions are identical with those described in Example 1, with the exception of the catholytecontaining, in place of 600 parts by weight of crystallised sodium sulphate, 250 parts by weight of potassium sulphate, Time wanted for electrolysis, working up and yield are as in Example 1. i a

Example 3 300 parts by Weight of d-ribonic acid lactone are reduced at a potassium-sodium-amalgam electrode under the same conditions as given, in Example 1, the catholyte, however, containing, in place of 600 parts by weight of sodium sulphate, a mixture of 300 parts by Weight of crystallised sodium sulphate and 125 parts by weight of potassium sulphate. Time wanted for electrolysis, working up and yield are as in Example 1.

Example 4 300 parts by weight of 'd-ribo-lactone are rewithin 3 hours, the said maximum, 'however,

being somewhat lower than in Example 1. Ac-

cordingly, after working up as described in Example 1, the yield of d-ribose-p-bromo-phenyllactone and parts by. weight of boric acid are added tothe. sodium sulphate solution. Electrolysis is continued for 5 hours at unchanged current density. The temperature of the c'atholyte is kept at about +12 C. by cooling, and the pfiis kept constant by dropwise addition of sulphuric acid, as described in Example 1 (Congo indicating papershould be greyish blue). For isolating d-arabinose the electrolyte is carefully concentrated in vacuo to 600 parts by volume. Sodium sulphate is precipitated by adding 1000 parts by volume of spirit to the weaklyCongoacid solution and, separated off by suction filtration. Afterconcentration of the filtrate to 1000- partsby volume, parts by weight of diphenylhydrazine-hydrochloride are added. Sodium hydroxide is added whilestirring until the solution is alkaline, whereupon the latter is acidified with acetic acid, After a short time, d-arabinosediphnyl-hydrazone precipitates. Precipitation is completed by stirring for 12 hours, whereupon the-mixture is passed through a suction filter. The crude diphenyl-hydrazone is Washed successively withn-ammonia, water, spirit and benzeneand then dried at 70 C. 162 parts by Weight of d-arabinose-diphenyl-hydrazone, having its melting point at 216 C., are obtained, from which d-arabinose may be obtained by cleavage with formaldehyde or benzaldehydeby the methods described by Neuberg and Wohlgemuth, Hoppe Seylers Zeitschrift fiir physiologische .Chemieflvol. 35, year 1902, p. 34-36.

ICIalmZ- '1. A process of reducing an inner lactone of a pentonic acid to a sugar which comprises subjectingan aqueous electrolyte containinga salt of a metal capable of forming an amalgam and containing said lactone to electrolysis treatment in an electrolysis cell, said reduction being effected at an amalgam cathode in'said cell, and maintaining said electrolyte acid-responsive to Congo indicator throughout said reduction of the lactone to the sugar.

2. A process according to claim 1, in which the lactone is d-ribono-lactone. i

3. A process according to claim 1 in which the lactone is d-arabono-lactone.

4. A process according to claim 1 in which the temperature throughout the reduction is maintained: in the range of 5-12 C. i

,5. A process according to'claim 1 in'which the electrolyticsolution contains a sulfate of an alkali metal. 6. A process according to claim 1 in which the lactone is di-ribono-lactone, and in which the electrolyte contains a sulfate of an alkali metal. 7. A process, according to claiml in which the :anodic, zone is maintained separate from the cathodic zone." 7 3 8. A processof reducing an inner lactone of a pentonic acid to a sugar which comprises subjecting an aqueous electrolyte containing a salt of an alkali metal capable of forming an amalgain and containing said lactone to electrolysis treatment in an electrolysis cell, said reduction being effected at an amalgam cathode in said cell, and maintaining said electrolyte acid-responsive to Congo indicator throughout said reduction of the lactone to the sugar.

9. A process of reducing ribono-lactone to ribose which comprises subjecting an aqueous electrolyte containing a salt of a metal capable of forming an amalgam, boric acid, and also containing said lactone, to an electrolysis treatment in an electrolysis cell, said reduction being effected at an amalgam cathode in said cell, and maintaining said electrolyte acid-responsive to Congo indicator throughout said reduction of the lactone to ribosel 10. A process of reducing ribono-lactone to ribose which comprises subjecting an aqueous electrolyte containing a salt of an alkali metal capable of forming an amalgam, boric acid, and containing said lactone, to electrolysis treatment HANS SPIEGELBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,227,706 Vaygouny May 29, 1917 2,303,210 Hales Nov. 24, 1942 OTHER REFERENCES Menon et al., Journal of the Chemical Society (London), 1929, page 303.

Frolich, Transactions of the Electrochemical Society, vol. LXXI, 1937, page 326. 

